Migrants have been banned from nightclubs in one German city after women complained the men had been slipping them date-rape drugs and accosting them in the bathroom.

Following similar waves of complaints of sexual assaults and harassment across Europe, women in Freiburg, on the edge of the Black Forest, say they can't go clubbing without being molested.

One claimed she was raped. Another migrant reportedly stabbed a bouncer.

A group of bar owners recently established a rule that if a migrant is kicked out of one establishment, he's not welcome in any across the city.

According to local newspaper Badische Zeitung, city hall is worried how the ban will look on the town, which considers itself a progressive enclave of southern Germany and open to asylum seekers.

Politicians are hoping to meet with the bar owners to discuss the ban.

"On the one hand it is clear that abuses or illegal acts are a no-go. On the other hand, you can't blame a whole group. You have to pick out the black sheep and ban them," Mayor Ulrich von Kirchbach told Badische Zeitung.

Some 3,000 migrants continue to stream over the border from Austria on average each day and if the trend continues Germany will have more than a million additional asylum seekers by the end of 2016.

This has led to some disturbing reports of sex attacks on the streets, such as the hundreds of allegations of rape and assault in Cologne on New Year's Eve.